[go] jsonrpc2 cleanup (#949)

* jsonrpc2 cleanup

* code review comments

* fix lint

* review feedback

Author: qmuntal

go/internal/jsonrpc2/frame.go

@@ -0,0 +1,92 @@
+package jsonrpc2
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"math"
+	"strconv"
+	"strings"
+)
+
+// headerReader reads Content-Length delimited JSON-RPC frames from a stream.
+type headerReader struct {
+	in *bufio.Reader
+}
+
+func newHeaderReader(r io.Reader) *headerReader {
+	return &headerReader{in: bufio.NewReader(r)}
+}
+
+// Read reads the next complete frame from the stream. It returns io.EOF on a
+// clean end-of-stream (no partial data) and io.ErrUnexpectedEOF if the stream
+// was interrupted mid-header.
+func (r *headerReader) Read() ([]byte, error) {
+	firstRead := true
+	var contentLength int64
+	// Read headers, stop on the first blank line.
+	for {
+		line, err := r.in.ReadString('\n')
+		if err != nil {
+			if err == io.EOF {
+				if firstRead && line == "" {
+					return nil, io.EOF // clean EOF
+				}
+				err = io.ErrUnexpectedEOF
+			}
+			return nil, fmt.Errorf("failed reading header line: %w", err)
+		}
+		firstRead = false
+
+		line = strings.TrimSpace(line)
+		if line == "" {
+			break
+		}
+		colon := strings.IndexRune(line, ':')
+		if colon < 0 {
+			return nil, fmt.Errorf("invalid header line %q", line)
+		}
+		name, value := line[:colon], strings.TrimSpace(line[colon+1:])
+		switch name {
+		case "Content-Length":
+			contentLength, err = strconv.ParseInt(value, 10, 64)
+			if err != nil {
+				return nil, fmt.Errorf("failed parsing Content-Length: %v", value)
+			}
+			if contentLength <= 0 {
+				return nil, fmt.Errorf("invalid Content-Length: %v", contentLength)
+			}
+		default:
+			// ignoring unknown headers
+		}
+	}
+	if contentLength == 0 {
+		return nil, fmt.Errorf("missing Content-Length header")
+	}
+	if contentLength > math.MaxInt {
+		return nil, fmt.Errorf("Content-Length too large: %d", contentLength)
+	}
+	data := make([]byte, contentLength)
+	if _, err := io.ReadFull(r.in, data); err != nil {
+		return nil, err
+	}
+	return data, nil
+}
+
+// headerWriter writes Content-Length delimited JSON-RPC frames to a stream.
+type headerWriter struct {
+	out io.Writer
+}
+
+func newHeaderWriter(w io.Writer) *headerWriter {
+	return &headerWriter{out: w}
+}
+
+// Write sends a single frame with Content-Length header.
+func (w *headerWriter) Write(data []byte) error {
+	if _, err := fmt.Fprintf(w.out, "Content-Length: %d\r\n\r\n", len(data)); err != nil {
+		return err
+	}
+	_, err := w.out.Write(data)
+	return err
+}